refactor(errors): derive FetchError and PixivError with thiserror

AGENTS.md

@@ -52,7 +52,7 @@ Docker: `docker build -t tgxmb .` then `docker run --rm -d --name tgxmb --env-fi
 
 ## Code Conventions & Common Patterns
 
-- **No anyhow/thiserror.** Errors are hand-rolled enums with manual `Display`/`source()`/`From` impls: `QueueError` (`Retryable { delay_seconds, payload }` / `Permanent`), `SendError` (Retryable/Permanent), `FetchError` (`Http`/`Json`/`Pixiv`/`Site`/`NotFound`/`Blocked`), `PixivError`, `Classification`. New errors should follow this pattern.
+- **Errors via `thiserror` derive** (no anyhow): the public, stringified errors — `FetchError` (`Http`/`Json`/`Pixiv`/`Site`/`NotFound`/`Blocked`) and `PixivError` — derive `thiserror::Error` with `#[from]` conversions; `Display`/`source()` come from the derive. The internal control-flow enums — `QueueError` (`Retryable { delay_seconds, payload }` / `Permanent`), `SendError` (Retryable/Permanent), `Classification`, `FallbackError` — carry no `Display` and are handled by direct variant matching. New errors should follow the same split: stringified/public errors derive `thiserror`, internal flow enums stay plain.
 - **Global state via `std::sync::LazyLock` statics**, not DI: `CONFIG`, `CHAT_STORE`, `TASK_QUEUE` in `handlers.rs`; shared reqwest `CLIENT` in `x-media/src/site/mod.rs`. `Bot` is passed/cloned into handlers; queue workers share the process-wide `send::BOT` (`LazyLock<Bot>`, force-initialized in `main` so a missing token fails at startup).
 - **Async**: tokio multi-thread runtime (`#[tokio::main]` default). All rusqlite I/O inside `tokio::task::spawn_blocking`. Long loops use `tokio::select!` with `tokio::sync::{watch, Notify}` stop/wake channels. No streams.
 - **Blocking sync primitives**: `parking_lot::Mutex` for hot caches, `tokio::sync::Mutex` for async-shared state (pixiv token cache), `AtomicBool` for feature gates.

Cargo.lock

@@ -2937,6 +2937,7 @@ dependencies = [
  "serde",
  "serde_json",
  "tempfile",
+ "thiserror",
  "tokio",
  "url",
  "zip",

crates/x-media/Cargo.toml

@@ -13,6 +13,7 @@ url = "2.5.2"
 bytes = "1"
 zip = "2"
 tempfile = "3"
+thiserror = "2"
 rand = "0.8"
 log = "0.4"
 tokio = { version = "1.40", features = ["time"] }

crates/x-media/src/site/mod.rs

@@ -4,7 +4,6 @@
 //! `PATTERN`, `enabled()` and `fetch_from_url()`; a future site plugs in by
 //! adding one guarded entry in [`fetch_once`].
 
-use std::fmt;
 use std::future::Future;
 use std::pin::Pin;
 use std::sync::LazyLock;
@@ -12,6 +11,7 @@ use std::sync::atomic::{AtomicBool, Ordering};
 use std::time::Duration;
 
 use regex::Regex;
+use thiserror::Error;
 
 pub mod bsky;
 pub mod pixiv;
@@ -183,84 +183,45 @@ pub fn site_id_from_key(key: &str) -> &'static str {
         .unwrap_or("unknown")
 }
 
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum FetchError {
-    Http(reqwest::Error),
-    Json(serde_json::Error),
-    Pixiv(PixivError),
+    #[error("http error: {0}")]
+    Http(#[from] reqwest::Error),
+    #[error("json error: {0}")]
+    Json(#[from] serde_json::Error),
+    #[error("pixiv error: {0}")]
+    Pixiv(#[from] PixivError),
     /// A site-specific error from a site that keeps its own error type.
     /// Permanent by default (sites that need retryable site errors convert
     /// them to [`FetchError::Http`] / [`FetchError::Transient`] before
     /// returning). Pixiv predates this and keeps the dedicated
     /// [`FetchError::Pixiv`] variant.
+    #[error("{site} error: {error}")]
     Site {
         site: &'static str,
+        #[source]
         error: Box<dyn std::error::Error + Send + Sync>,
     },
+    #[error("not found")]
     NotFound,
+    #[error("blocked")]
     Blocked,
     /// The post exists but its content is withheld (twitter NSFW /
     /// age-restricted tweets come back as an empty `{}` from syndication).
+    #[error("content withheld (sensitive)")]
     Sensitive,
     /// A download exceeded the caller's size cap (see [`download_media_limited`]).
+    #[error("media too large")]
     TooLarge,
     /// A transient server-side failure (429 / 5xx); [`fetch`] retries these.
+    #[error("transient: {0}")]
     Transient(String),
     /// A local I/O failure while streaming a download to disk
     /// (see [`download_media_to_file`]).
+    #[error("io error: {0}")]
     Io(std::io::Error),
 }
 
-impl fmt::Display for FetchError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            FetchError::Http(e) => write!(f, "http error: {e}"),
-            FetchError::Json(e) => write!(f, "json error: {e}"),
-            FetchError::Pixiv(e) => write!(f, "pixiv error: {e}"),
-            FetchError::Site { site, error } => write!(f, "{site} error: {error}"),
-            FetchError::NotFound => write!(f, "not found"),
-            FetchError::Blocked => write!(f, "blocked"),
-            FetchError::Sensitive => write!(f, "content withheld (sensitive)"),
-            FetchError::TooLarge => write!(f, "media too large"),
-            FetchError::Transient(message) => write!(f, "transient: {message}"),
-            FetchError::Io(e) => write!(f, "io error: {e}"),
-        }
-    }
-}
-
-impl std::error::Error for FetchError {
-    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
-        match self {
-            FetchError::Http(e) => Some(e),
-            FetchError::Json(e) => Some(e),
-            FetchError::Pixiv(e) => Some(e),
-            FetchError::Site { error, .. } => Some(error.as_ref()),
-            FetchError::NotFound | FetchError::Blocked | FetchError::Sensitive => None,
-            FetchError::TooLarge => None,
-            FetchError::Transient(_) => None,
-            FetchError::Io(e) => Some(e),
-        }
-    }
-}
-
-impl From<reqwest::Error> for FetchError {
-    fn from(e: reqwest::Error) -> Self {
-        FetchError::Http(e)
-    }
-}
-
-impl From<serde_json::Error> for FetchError {
-    fn from(e: serde_json::Error) -> Self {
-        FetchError::Json(e)
-    }
-}
-
-impl From<PixivError> for FetchError {
-    fn from(e: PixivError) -> Self {
-        FetchError::Pixiv(e)
-    }
-}
-
 /// Shared HTTP client (browser User-Agent) for twitter/bsky fetches and
 /// [`download_media`].
 pub(crate) static CLIENT: LazyLock<reqwest::Client> = LazyLock::new(|| {

crates/x-media/src/site/pixiv/api.rs

@@ -8,11 +8,11 @@ use super::model::{IllustrationModel, TypeModel, UgoiraMetadataModel};
 use crate::media::Media;
 use crate::site::FetchError;
 use std::env;
-use std::fmt;
 use std::io::Read;
 use std::sync::LazyLock;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::time::{Duration, SystemTime};
+use thiserror::Error;
 
 const AUTH_TOKEN_URL: &str = "https://oauth.secure.pixiv.net/auth/token";
 const APP_API_URL: &str = "https://app-api.pixiv.net";
@@ -23,53 +23,24 @@ const APP_USER_AGENT: &str = "PixivIOSApp/7.13.3 (iOS 14.6; iPhone13,2)";
 /// Token refresh safe margin (seconds).
 const TOKEN_REFRESH_SAFE_MARGIN: u64 = 300;
 
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum PixivError {
     /// No refresh token available (PIXIV_REFRESH_TOKEN unset).
+    #[error("pixiv: no authentication")]
     NoAuth,
-    Http(reqwest::Error),
-    Json(serde_json::Error),
+    #[error("pixiv http error: {0}")]
+    Http(#[from] reqwest::Error),
+    #[error("pixiv json error: {0}")]
+    Json(#[from] serde_json::Error),
     /// Non-2xx HTTP status from the app API. The code lets [`crate::site::fetch`]
     /// retry only transient classes (429 / 5xx) instead of burning attempts on
     /// permanent 4xx (bad token, forbidden, not found).
+    #[error("pixiv status {0}")]
     Status(u16),
+    #[error("pixiv api error: {0}")]
     Api(String),
 }
 
-impl fmt::Display for PixivError {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            PixivError::NoAuth => write!(f, "pixiv: no authentication"),
-            PixivError::Http(e) => write!(f, "pixiv http error: {e}"),
-            PixivError::Json(e) => write!(f, "pixiv json error: {e}"),
-            PixivError::Status(code) => write!(f, "pixiv status {code}"),
-            PixivError::Api(message) => write!(f, "pixiv api error: {message}"),
-        }
-    }
-}
-
-impl std::error::Error for PixivError {
-    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
-        match self {
-            PixivError::Http(e) => Some(e),
-            PixivError::Json(e) => Some(e),
-            _ => None,
-        }
-    }
-}
-
-impl From<reqwest::Error> for PixivError {
-    fn from(e: reqwest::Error) -> Self {
-        PixivError::Http(e)
-    }
-}
-
-impl From<serde_json::Error> for PixivError {
-    fn from(e: serde_json::Error) -> Self {
-        PixivError::Json(e)
-    }
-}
-
 /// Native pixiv app-API client.
 pub struct PixivAPI {
     refresh_token: String,